Basidiomycota
This
division has many features in common with the Ascomycota: mycelia with
chitinous cell walls that are regularly septate, presence of an extended
dikaryon stage, yeast stage and presence of macroscopic fruiting bodies, in
some taxa, and conidia are produced if an asexual stage is present. As in the
Ascomycota and Zygomycota, the characteristic that defines this subdivision is
the sexual spore stage. The sexual spores produced are basidiospores
that are typically borne, exogenously, on horn-like sterigmata
(sing.=sterigma) of basidia (sing.= basidium) (Fig. 1). The morphology
of the basidium, however, is variable and a few of the variations are shown in
the micrographs below (Figs. 2-4), and the variations observed below were once
thought to be of considerable significance in the phylogeny of the
Basidiomycota.
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Figure 1:
Unicellular basidium, with four sterigmata and basidiospores. Basidium
illustrated to the left is commonly used as representative of the typical
basidium.
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Figure 2:
Cruciate-septate basidium. This basidium is divided into four chambers. The
basidium is named for the "cross" that can be seen when viewed,from
above, through the microscope.
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Figure 3:
Transversely septate basidium. This basidium resembles hyphal cells, with
sterigmata . Because of its lack of differentiation, this was once considered
to be a primitive basidium.
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Figure 4: Tunning
fork basidium. The basidium is named for its obvioius resemblance to a
tunning fork. This basidium produces only two basidiospores.
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Figure 5:
Transversely septate basidiospores germinating from a rust teliospore.
Basidiocarp is absent.
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Three
classes are currently recognized:
- Class: Basidiomycetes
- Class: Uredinomycetes
- Class: Ustomycetes
